An indoor unit of an air-conditioning apparatus is installed in a room (in a room of a house or office) subjected to air conditioning. Indoor air sucked through the air inlet exchanges heat in a heat exchanger with a refrigerant circulated in a refrigeration cycle so as to heat the indoor air during heating operation and cool the indoor air during cooling operation. The indoor air heated or cooled is blown into the room through the air outlet. For this purpose, a fan and a heat exchanger are housed in an indoor unit main body.
Among many types of the existing indoor units of the air-conditioning apparatuses, it is well-known that some types of the indoor units such as a wall-installation type, which have an elongated air outlet, and a ceiling concealing type, which blows air in a single direction, use cross flow fans (also referred to as tangential fans or transverse fans) as their air sending device. With respect to an airflow flowing from an air inlet to an air outlet in the indoor unit of the air-conditioning apparatus, a heat exchanger is disposed upstream of the cross flow fan, that is, the heat exchanger is disposed between the air inlet and the cross flow fan, and the air outlet is positioned downstream of the cross flow fan. The length of the air outlet of the indoor unit in the longitudinal direction is substantially the same as the entire length of the cross flow fan in the longitudinal direction (rotational axis direction). Components such as drive motor and support portions that support the rotating shaft of the cross flow fan are disposed further to the outside in the longitudinal direction of the both ends of the cross flow fan with a space between these components and each end of the cross flow fan.
The cross flow fan (simply referred to as “fan” hereafter) includes a plurality of individual impeller units connected to one another in the rotational axis direction. In each of the individual impeller units, a plurality of blades, each of which is curved so as to have an arc shape in section, are secured to an annular (ring-shaped) support plate, which is a flat plate having outer and inner diameters. The blades are inclined by a predetermined angle relative to the support plate and secured to the support plate so as to form concentric annular shapes. A discoid end plate is secured to ends of the blades of the individual impeller unit at one end in the rotational axis direction. The rotating shaft supported by a bearing portion of the indoor unit main body is attached to the end plate. The individual impeller unit at the other end in the rotational axis direction includes an end plate with a boss. Unlike the support plates in other portions, the end plate with a boss has a boss portion at its center. The motor rotating shaft of the drive motor is secured to the boss. When the drive motor rotary drives, the fan is rotated about the rotational axis, which is the center of the rotating shaft. The blades are inclined so that their respective outer circumferential blade ends are positioned at the front in the rotational direction.
Hereafter, each of the individual impeller units arranged in series in the rotational axis direction is referred to as a “unit” of the fan for the convenience of description. The individual impeller unit located at each end of the fan in the rotational axis direction is referred to as an “end unit.”
As the fan is rotated, indoor air is sucked into the indoor unit main body of the air-conditioning apparatus through the air inlet. The sucked air becomes conditioned air, the temperature of which has been adjusted as described above while passing through the heat exchanger. The conditioned air crosses the fan, and after that, passes through an air path that extends to the air outlet and is blown into the room through the air outlet formed in a lower portion of the indoor unit main body.
The pressure inside the indoor unit is lower than the atmospheric pressure because of frictional resistance (pressure loss) applied to air while the air is passing through the heat exchanger. The fan provides energy to the airflow so that the airflow surpasses the atmospheric pressure, thereby blowing the air from the air outlet. However, when the energy provided to the airflow from the fan is not sufficient to surpass the atmospheric pressure, the pressure inside the indoor unit becomes lower than the atmospheric pressure outside the indoor unit. In this case, indoor air is sucked into the indoor unit through the air outlet. This phenomenon is referred to as “reverse suction.”
Reverse suction tends to occur near the both ends of the fan in the rotational axis direction. The reason of this is as follows.
At each end of the fan in the rotational axis direction, an end plate, which is part of the individual impeller unit as a rotating body, and a side wall of the indoor unit main body are disposed. The side wall defines a side surface of an air path and is disposed further to the outside than the end plate so as to oppose the side plate. The end plate and the side plate are spaced apart from each other by about 5 mm so as to prevent the occurrence of rotational friction, which may otherwise occur due to contact of the end and side plates with each other. A space formed between the end plate and the side wall opposite the end plate is positioned at the outside of each end of the fan in the rotational axis direction. This space is in an atmosphere in which the pressure is lower than the atmospheric pressure due to the pressure loss while the air is passing through the heat exchanger. Thus, it is considered that reverse suction tends to occur due to the pressure difference between the pressure in the space and the atmospheric pressure outside the indoor unit. When reverse suction occurs, the air volume of the entire fan is reduced, thereby degrading the performance of the fan. Furthermore, turbulence of the airflow is caused by reverse suction, thereby increasing noise. When reverse suction occurs during cooling operation, droplets of condensed water may scatter in the room (this scattering is referred to as “scattering of water droplets”). The scattering of water droplets is a phenomenon in which high-humidity indoor air having flowed into the indoor unit due to reverse suction is condensed through its contact with low-temperature wall surfaces inside the indoor unit, and the condensed water then becomes water droplets and may be scattered into the room. In particular, when draft resistance is increased by, for example, dust accumulated in the air inlet, sufficient energy is unlikely to be provided by the fan, and accordingly, occurrence of reverse suction is facilitated.
There is an example of a structure in order to prevent above-described reverse suction. In this structure, a member having an outer circumstantial surface is attached to each end of the cross flow fan in the rotational axis direction. The size of the member is increasing toward each side surface so as to form a bell shape. With the bell-shaped member, the gap between each end of the fan in the rotational axis direction and a space, in which the pressure is lower than the atmospheric pressure, formed outside the end of the fan is reduced so as to prevent the reverse suction (for example, see Patent Literature 1).